The present invention relates to a method for controlling pink bollworm by mating disruption of the pink bollworm to thus control the proliferation thereof.
Pink bollworm is a harmful insect which inflicts serious damage to the cotton plant and the control thereof has been a worldwide problem. There have been proposed techniques for controlling the insect by mating disruption of the imagines thereof (disturbance of any male-female communication) by the use of the sex pheromone of the pink bollworm or analog thereof. For instance, Environ. Entomol., 1, p. 645 discloses a method which makes use of Z-7-hexadecenyl acetate as an effective component and Science, 196, p. 904 discloses a method which makes use of gossyplure (a 1:1 mixture of Z,Z-7,11-hexadecadienyl acetate and Z,E-7,11-hexadecadienyl acetate), which is the sex pheromone of the pink bollworm, as an effective component. These effective components are very expensive and, therefore, there has been desired for the development of a control composition which is highly effective for disturbing the male-female communication of the insects in a small amount.
A control composition which can satisfy such requirements comprises the mixture of sex pheromone and an attraction-inhibitory substance. Upon practical use of the control composition, the composition loaded in a polyethylene tube is applied in a cotton field and thus the effective components are gradually allowed to emit into the air through the wall of the polyethylene tube. More specifically, this control composition is an agent used in the form of a sustained release formulation provided with a barrier layer.
However, the sex pheromone and the attraction-inhibitory substance in the control composition are not always released in proportion to the predetermined mixing ratio. The sex pheromone and the attraction-inhibitory substance are different from one another and, therefore, the vapor pressures thereof are also different. However, the difference between the vapor pressures of these compounds is very small since the former is an acetate derivative of an unsaturated aliphatic compound and the latter is an alcohol derivative of the same unsaturated aliphatic compound. For this reason, it is difficult to consider that the variation in the rate of release is ascribed to the difference in the vapor pressure. In fact, if the control composition is allowed to emit into the air without using any barrier layer, it has been confirmed that the sex pheromone and the attraction-inhibitory substance in the control composition are approximately released in proportion to the predetermined mixing ratio. Under such circumstances, the inventors of this invention have conducted various studies and have found out that the sex pheromone and the attraction-inhibitory substance in the control composition are not always released in proportion to the predetermined mixing ratio since they are not always allowed to emit through the barrier layer at the same rates.
For instance, when a control composition which comprises 100 parts by weight of a sex pheromone, i.e., Z,Z/Z,E-7,11-hexadecadienyl acetate (a mixture of Z,Z-7,11-hexadecadienyl acetate and Z,E-7,11-hexadecadienyl acetate; the same expression will be used hereinafter) and one part by weight of an attraction-inhibitory substance, i.e., Z,Z/Z,E-7,11-hexadecadienyl alcohol (a mixture of Z,Z-7,11-hexadecadienyl alcohol and Z,E-7,11-hexadecadienyl alcohol; the same expression will be used hereinafter) is loaded in a polyethylene tube and the resulting formulation is used for releasing these components into the air, the composition released into the air through the polyethylene barrier comprises 100 parts by weight of Z,Z/Z,E-7,11-hexadecadienyl acetate and 0.5 part by weight of Z,Z/Z,E-7,11-hexadecadienyl alcohol. For this reason, the composition does not ensure sufficient control effect. In particular, when the population of the pink bollworm is high, the control effect of the composition through disturbance of the male-female communication is not sufficient.